The present invention relates to electrical connectors and in particular, to contact pins for use in releasable pin and socket contacts.
Pin and socket contacts are employed in a wide variety of electrical connectors such as flat conductor cable connectors, edgeboard connectors, and connectors with coaxial cable terminations, for example. In such connectors, a series of pins are arranged on a male connector member and corresponding sockets are arranged on a female connector member. The pins and sockets are dimensioned for cooperative frictional engagement to retain the pins in place even after repeated disconnections from the sockets.
One common form of pin now in use is a so-called "twist pin" which comprises a core cable of one or more strands or wires formed of soft copper, e.g., oxygen free copper (OFC), surrounded by one or more clusters of beryllium copper (Be Cu) spring wires, the latter being helically wound around the core wires. The pin is formed such that the outer wires form a bulge intermediate the pin ends. A twist pin of this type is described, for example, in U. S. Pat. No. 3,319,217 issued to Phillips on May 9, 1967. The maximum cross-sectional area of the pin in its uncompressed state is greater than the inner diameter of the socket so that when the pin is inserted into the socket, the outer wires are resiliently compressed to produce the frictional interconnection between the pin and socket.
Beryllium copper is chosen as the material for the outer wires (i.e., the socket-engaging wires) due to its high degree of resiliency, it being felt that not only does such resiliency promote a secure mechanical engagement, but also assures a reliable electrical conductive connection as the pin rebounds to bear against the socket along a substantial interface after engagement is effected.
In practice, the forces required to engage a given pin and socket can be over 5 ounces of force per contact. While such a force per contact is not significant, per se, it will be appreciated that in a connector employing over a hundred contacts (e.g., over 184 contacts in one commercial connector), the overall mating force required to mate the male and female connector members can be very high, even when the contacts have been lubricated, thereby imposing a burden on the field personnel and or limiting, in effect, the number of contacts which are employed in a connector. Any attempt to alleviate this inconvenience must not result in a reduction in the separation force (i.e., the force needed to separate the pins) below a given minimum value (e.g., 0.5 oz.). (Otherwise, inadvertent separation of the connector may occur.) Low values suggest marginal normal force conditions which would lead to failure. Unless a minimum normal force is present, the electrical connection across the separatable interface may exhibit excessive constriction resistance.
Efforts to deal with this condition have included the examination of various non-conventional pin configurations depicted in cross-section in FIGS. 1-3. For example, coreless pins were considered in which the center or core cable is omitted. Rather, the pin comprises a plurality of helically wound cables, each cable formed of a plurality of wound wires of Be Cu of 0.0035 inch diameter (see FIG. 1). In one case, three cables of three wires each were proposed (FIG. 1); in another case three cables of four wires each were proposed; in another case four cables of three wires each were proposed. It was concluded that those designs would not solve the problem, but rather would be characterized by undesirably high engagement forces, among other disadvantages.
In another example, there were tested pins formed of a core of three helically wound wires of OFC (0.005 inch diameter) around which are helically wound 11 or 12 wires (FIG. 2) of BeCU (0.0035 inch diameter). However, undesirably high engagement forces resulted. Moreover, during the fabrication process, the outer wires would not achieve a proper bulge configuration.
In a further example, a pin was tested comprising a plurality of BeCu wires (0.005 inch diameter) helically wound around three OFC wires (0.0035 inch diameter). In one case five wires of BeCu were considered (FIG. 3); in another case three wires of BeCu were considered. Performance and quality for this type of pin were completely unsatisfactory.
It is, therefore, an object of the present invention to provide a contact pin which is characterized by reduced engagement forces, while maintaining a preselected minimum separation force.
It is another object of the invention to provide such a contact pin which does not depart from conventional pin configuration.
It is a further object of the invention to provide such a contact pin which creates ample electrical engagement with the socket.